The present invention relates to a battery apparatus for controlling plural high energy battery cells connected in series and its control method, and more particularly to a battery apparatus which is suitable for a low order control device which controls a battery module having plural battery cells connected in series and a high order control device for giving instructions to plural low order control devices.
For example, Japanese Patent Laid-Open Publication No. 10-322925 describes a conventional battery apparatus which is comprised of plural battery cells connected in series as a battery module, plural battery modules being connected in series, and a low order control device disposed for each battery module, a command being sent from a high order control device to the low order control device. The low order control devices monitor the states of the battery cells possessed by the corresponding battery modules. The low order control devices disposed in the same quantity as that of the battery modules are electrically connected in series via the battery modules, a signal is transmitted between the high order control device and the low order control devices and between the low order control devices by an isolating unit such as a photocoupler in a configuration that no affect is caused by a potential difference between the control devices.
The low order control device adjusts the capacity of the battery cells as described in Japanese Patent Laid-Open Publication No. 2000-92732 for example. The capacity adjustment means the reduction of a voltage difference between the battery cells by having a resistor connected in parallel to the battery cells via a switch, and when the battery cells measured by a voltage detection circuit have a high voltage, driving the switch to partly discharge the amount of electricity stored. Particularly, a lithium-ion battery, which has amorphous carbon with high relevancy between an open-circuit voltage and a remaining capacity as an anode active material, can effectively equalize the capacity of each battery cell by reducing a voltage difference between the battery cells.
In recent years, there has been used an ultra capacitor which can store the same amount of electricity as the secondary battery and has less degradation in service life as compared with the secondary battery. The ultra capacity adopts a method of equalizing the voltage between the capacitor cells as described in Japanese Patent Laid-Open Publication No. 2001-37077 for example. This method provides a circuit which connects a switch in parallel to the capacitor cells to detect the voltage of the capacitor and bypasses part of electricity to the switch. It is similar to the aforesaid Japanese Patent Laid-Open Publication No. 2000-92732.
The low order control device detects a voltage of the battery cell or the capacitor cell, and when the voltage is high, operates the switch to adjust the capacity. Meanwhile, the high order control device sends an instruction signal to make the low order control device to adjust the capacity. In Japanese Patent Laid-Open Publication No. 2000-92732, an open-circuit voltage of each battery cell of the battery module is measured when the low order control device is activated, and the measured value is transmitted to the high order control device. The high order control device calculates a reference voltage value at the time of capacity adjustment from the value of open-circuit voltage obtained from all the low order control devices and gives instructions to the low order control devices again.
Problems to be remedied by the present invention are following three. First, it is a cost problem. The secondary battery and the ultra capacitor are expected to be used for a battery apparatus for the electric car or the hybrid electric car, but it is demanded that their costs are reduced for mass production. For the cost reduction of the battery apparatus, it is necessary to reduce the cost of the battery cell or the capacitor cell itself and also to reduce the costs of the plural low order control devices. To achieve it, it is effective to have the low order control devices as ICs (integrated circuits).
However, even when the low order control device is ICed, the isolating unit such as a photocoupler used for the signal transmission between the high order control device and the low order control devices and between the low order control devices remains as it is. For example, when a lithium-ion battery is used, it is assumed that the battery cell has a voltage of 3.6V and 40 batteries are connected in series, this potential difference is 144 V between the battery in the lowest potential and the battery in the highest potential. In this example, if four battery cells are grouped into each battery module, ten low order control devices are provided, and the respective low order control devices are provided with about two isolating units for input and output. Thus, a total of 20 isolating units are necessary, and there is a disadvantage that the control devices cost high.
Second, there is a problem of reliability. There is a possibility that an external interference enters the instruction signal due to noise produced by an inverter device or the like which is connected as a load on the battery apparatus. Therefore, there is a problem that the reliability of the signal transmission is decreased when instructions are given from the high order control device to the low order control devices because of the external interference.
Third, there is a problem of accuracy of detecting a voltage. The plural low order control devices are provided with a voltage detection circuit and detect a voltage of the battery cells disposed in the corresponding battery modules, but the battery voltage detection needs highly accurate performance with merely an allowable error of several tens of mV. A lithium-ion battery, which uses amorphous carbon for the anode active material, has an obvious relation between the open-circuit voltage and the remaining capacity as compared with another battery such as a nickel metal hydride battery. But, it is said that even the lithium-ion battery has an allowable error of xc2x150 mV or less in voltage equalization for the capacity adjustment. Conversion of a voltage of 50 mV is equivalent to about 5% of the remaining capacity of the lithium-ion battery. The highest voltage of the lithium-ion battery is about 4.2V but the aforementioned 50 mV is 1.2% with respect to 4.2%, indicating that the accuracy of voltage detection is very strict.
In order to achieve the highly accurate voltage detection, an A/D converter of ten-odd bits is generally used, but the accuracy of the A/D converter depends on the accuracy of a reference voltage source. Therefore, the low order control device needs a highly accurate reference voltage source with an extremely small error (e.g., about xc2x125 mV). Since each low order control device is connected to the battery module having a different potential, it is difficult to share the highly accurate reference voltage source with the plural low order control devices. Specifically, to achieve the highly accurate voltage detection, there was a problem that the cost of the reference voltage sources which are respectively provided for the plural low order control devices became high.
A first object of the present invention is to provide a battery apparatus which has a quantity of isolating units decreased and is provided with low-cost control devices.
A second object of the invention is to provide a control method of a battery apparatus, which reduces the influence by external interferences such as noise and can make the signal transmission with improved reliability.
A third object of the invention is to provide an inexpensive battery apparatus which can achieve the highly accurate voltage detection.
(1) In order to achieve the first object, the invention is directed to a battery apparatus comprising plural battery modules connected in series which have plural battery cells connected in series; plural low order control devices which are disposed in correspondence with the plural battery modules and control the plural battery cells configuring the battery modules; and a high order control device which controls the plural low order control devices, wherein there are provided an isolating unit or a potential converting unit which connects the input terminal of the low order control device in the highest potential among the plural low order control devices, the output terminal of the low order control device in the lowest potential, and the high order control device; and an interruption element which is disposed between the output terminal of the low order control device and the battery cells in the battery module on a low potential side and prevents the discharge current of the battery cells in the battery module; and terminals related to the input and output of a signal are electrically connected in a non-isolated state among the plural low order control devices.
By configuring as described above, the quantity of the isolating units can be reduced, and the low-cost control device can be obtained.
(2) In the item (1) above, it is preferable that the input terminal of the low order control device is electrically connected to the battery cell on a high potential side among the battery cells within the battery module being controlled by the low order control device.
(3) In the item (2) above, it is preferable that the plural low order control devices, the isolating unit or the potential conversion unit which is disposed on the low order control devices in the highest and lowest potentials, and the high order control device are mounted on the same package, and power is supplied from the outside of the package to the high order control device.
(4) To achieve the first object, the invention is directed to a control method of battery cells which is provided with plural battery modules connected in series which have plural battery cells connected in series; plural low order control devices which are disposed in correspondence with the plural battery modules and control the plural battery cells configuring the battery modules; and a high order control device which controls the plural low order control devices, wherein the high order control device compares a signal transmitted to the low order control device in the highest potential with a signal returning from the low order control device in the lowest potential, and transmits the next instruction when it is determined to be normal.
The aforementioned method enables to improve the reliability by reducing an influence due to the external interference such as noise.
(5) In the item (4), it is preferable that the low order control device detects the states of the plural battery cells of the battery module controlled by the low order control device, takes a logical add or a logical product of the state detection signal and an input signal transmitted from the low order control device in a high potential, and outputs the result to the low order control device in a low potential; and the high order control device determines a defect of the battery apparatus according to the signal returning from the low order control device in the lowest potential.
(6) In the item (4), it is preferable that the low order control device performs the capacity adjustment to discharge the remaining capacity of the battery cell when the voltage of the battery cells in the battery module is higher than a reference value, and the low order control device having completed the capacity adjustment gets into a sleep mode.
(7) To achieve the third object, the invention is directed to a battery apparatus, comprising plural battery modules connected in series which have plural battery cells connected in series; plural low order control devices which are disposed in correspondence with the plural battery modules and control the plural battery cells configuring the battery modules; and a high order control device which controls the plural low order control devices, wherein there are provided a voltage detecting unit which detects a voltage of the plural battery cells within the battery modules, and an error calibration terminal which calibrates an error of the voltage detecting unit.
By configuring as described above, the highly accurate voltage detection can be achieved, and the cost reduction can also be achieved.
(8) In the item (7), it is preferable that the voltage detecting unit is an A/D converter, and the low order control device compensates an output value by previously giving a digital value to the error calibration terminal of the A/D converter.
(9) In the item (8), it is preferable that the A/D converter comprises an integration unit which integrates a unit amount of electricity according to the number of pulses; a comparing unit which compares the integral value of the integration unit with the voltage of the battery cell and stops the pulse; a counter unit which outputs the number of pulses when the pulse is stopped by the comparing unit; and a compensation unit which compensates output of the counter unit according to the digital value given to the terminal for calibrating the error.
(10) In the item (9), it is preferable that the compensation unit changes a counted value of the counter unit according to the digital value given to the error calibration terminal to compensate an offset of the A/D conversion and changes a width of the pulse to compensate a gain of the A/D conversion.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.